Przeciążony operator +

class cMatrix
{
    int kolumny;
    int wiersze;
    friend istream & operator >>( istream & str, cMatrix & x );
    friend ostream & operator <<( ostream & str, cMatrix & x );
   
public:
    vector < vector < int >> vec;
   
    cMatrix();
    cMatrix( int a, int b );
    cMatrix( const cMatrix & M )
        : kolumny( M.kolumny )
         , wiersze( M.wiersze )
    { }
   
};